Altering a 250 two stroke powerband?

LuckyStar64

LuckyStar64

PR Addict
I started thinking about this when I was looking to run MX suspension on a KDX 220. It seems like everybody is doing bore- up 125's. It works pretty well obviously, but has anybody gone the other way? As in toning down a 250 two stroke? Reducing the hit via less compression, smaller carb, and a flywheel weight. Cutting down on the vibration (balanced crank maybe?), and getting 4-stroke smooth power out of it? I like 125's and the derivatives, but I'd prefer a less spastic ride w/o having to go to a 4-stroke. I'd like a bike that's easy to ride for hours on. Seems like the thing would be super durable in a detuned state. --L*64
 
Did you say de-tune????? I have always liked the 250 2stroke power but it's tricky on dry hard-packed! I have never thought about de-tuning a bike, maybe a flywheel weight or little options like that
 
My goal was actually to make my power delivery as similar to a 4T as possible. I started with a YZ-250 which I sent to Eric Gorr which came back a 295, he also will port your cylinder and do head work to have the powerband you want. Mine has increased low end, smoother mid-range hit and the about the same as stock on the top end. I added an 11oz fly wheel weight, V-Force 3's, Pro-Circuit exhaust. The result is you can lug in a high gear on hardpack, but it still winds up fast and screams when you want it to.
 
When I finished restoring my 1984 RM250, it had such a brutal hit that I had trouble riding it. It was a wheelie monster out of turns if you got any traction; if no traction it would slide out.

I sent the topend to Eric Gorr asking for porting for his "more-better" powerband that has a smoother hit and longer, broader power. It worked great. I can now rollon the power better and more controllably, and ride the bike longer because it's not ripping my arms out. But it's still super fast.

I would go with porting and a flywheel weight. Also, if you do a big-bore 250 they are supposedly longer, broader, less hit powerbands.
 
Years ago, I spent a good deal of time on an RMX250. It was largely because the guy whose bike it was wanted to ride the KX250 I had at the time. I remember being able to ride the bike so smoothly-- I could go faster on it than anything else-- and it didn't seem like I was trying. If I remember correctly-- besides having different internal gears, the RMX motor had RM250 engine cases. I was wondering what the heck they did to the thing to get it so tame compared to the RM motor. Lowered ports, a milled out head, heavier flywheel. I loved the way that bike motored seamlessly around a track. It had "four stroke" like power from a two stroke. ---L*64
 
Yup,

Got my eye on a 2005 KX250 (seems to be all I can come up with for payment at the moment) that I would love to bolt on a 301cc cylinder (plan to keep an original cylinder around just in case) I saw from kustom-kraft.com (may check into this other guy you guys mention) and add a flywheel weight to it. Reasoning? I did very much like the power delivery of the KTM 300 EXC I believe it was, that I rode at a BC KTM ride day. Very 450ish in terms of the gear and shifts I would use. EXC was toned down to an extent I am sure from a SX version, but was plenty fast for what I was trying to do.

Just my thinking. Have no expereince in how it will turn out, but have read about this on KX's and reviews were good.... 125's, 140's, 150's are two much work for me. Fun for a moment, but wouldn't be a long ride type of thing for me...
 
PitRacer said:
When I finished restoring my 1984 RM250, it had such a brutal hit that I had trouble riding it. It was a wheelie monster out of turns if you got any traction; if no traction it would slide out.

I sent the topend to Eric Gorr asking for porting for his "more-better" powerband that has a smoother hit and longer, broader power. It worked great. I can now rollon the power better and more controllably, and ride the bike longer because it's not ripping my arms out. But it's still super fast.

I would go with porting and a flywheel weight. Also, if you do a big-bore 250 they are supposedly longer, broader, less hit powerbands.
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They are!
 
If anyone is curious how a 300 2T with a flywheel weight is you are more than take a spin on mine if we can find somewhere to meet up that isn't killer distance for me. I have an Eric Gorr (most will agree best in the business) 295, more-better with the flywheel weight.
 
Ive definately thought about all the above. I like the idea of a 250 port and polish with a flywheel weight. I love my 250f but I dont need a 450f. 125's are fun, 144 150s Im sure are even more fun. Id really like a 200 but Im not a ktm fan. Its always seemed more logical to me to tone down a 250 to be smooth then it would be to go with a overbore on a 125. It seems now some exotic brands are starting to explore bikes between the 125 250. Im guessing that 310 is a handful! What sucks is it appears that 2 strokes have gone up in value.
 
Scotty810 said:
It's probably due to the vets of this site! :)
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No doubt, speaking of, my neighbor made a score last night on a 01 YZ-125. If you bought a used 2011 it would not be as new as this one. The suspension is not even broken in yet, stock sprockets and chain, stock graphics in great shape and it still has the warning stickers on the fender.
 
If you want a two stroke that rides like a four stroke, just ride Maico's 700 cc monster. The power on that thing will be about as broad as it gets! Just don't ever leave 2nd gear.
 
I think my experience on the 4 stroke machines taught me throttle control and now after doing the four stroke thing for 5 years it makes the the 2t more manageable. if that makes sense...
 
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